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What does bad file descriptor mean?
“Bad file descriptor” means that we tried to perform an operation on a file descriptor which is not active, probably closed beneath someone’s feet. There is no file path associated with it anymore.
Why do I get bad file descriptor?
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa). There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren’t any processes to manipulate.
What does FD_ISSET return?
The FD_ISSET() macro returns a non-zero value if the bit for the file descriptor fd is set in the file descriptor set pointed to by fdset , and 0 otherwise. On successful completion, select() returns the total number of bits set in the bit masks. Otherwise, -1 is returned, and errno is set to indicate the error.
What is a file descriptor C?
What is the File Descriptor? File descriptor is integer that uniquely identifies an open file of the process. File Descriptor table: File descriptor table is the collection of integer array indices that are file descriptors in which elements are pointers to file table entries.
How to check if FD is a valid file descriptor?
fcntl (fd, F_GETFD) is the canonical cheapest way to check that fd is a valid open file descriptor. If you need to batch-check a lot, using poll with a zero timeout and the events member set to 0 and checking for POLLNVAL in revents after it returns is more efficient.
How to check if a given file descriptor is stored in a?
The descriptor is typically just a small integer like 6 and your libc can choose to reuse that number if you close the file and open a new one later. Instead, you should consider using dup () to copy the file descriptor.
Which is the cheapest way to get a file descriptor?
GitHub STOP HELPING ICE fcntl (GETFL) is probably the cheapest and least likely to fail operation you can perform on a file descriptor. In particular, the specification suggests that it cannot be interrupted by signals, nor is it affected by any sort of lock held anywhere.
How to check if a given resource handle is still valid?
With that said, the operation “check if a given resource handle is still valid” is almost always fundamentally incorrect. After a resource handle is freed (e.g. a fd is close d), its value may be reassigned to the next such resource you allocate.